Hiya,
I've got a pic of lowland truncata and several types of highland truncata on my website.
Obviously the first difference is that one is a lowland variant which likes it hot, and the other is a highland variant that likes warm days and cool nights.
On a morphological level, the lowland variant has green pitchers with either a reddy/brown or striped peristome, and the highland variant has numerous pitcher colours, from green, yellow, orange, purple, red and black. The highland variant can also have a more pronounced peristome. It is also claimed that the highland form is larger. In my experience, the highland form is a faster grower than the lowland form.
Hamish